The present invention concerns a covering for an airbag module accommodated in the door lining and/or in the instrument panel of a vehicle. The module has a main part of plastic comprising an airbag-attaching component and an airbag-covering component. The airbag-covering component can optionally be covered with expanded plastic. The module has a cover of real or imitation leather. There is at least one area in the form of a flap that can be ripped open in the vicinity of the airbag-covering component. The rip-open area is demarcated by a break-open line, constituted by a weakening of the material, and by a hinging line.
In most of the airbag-module coverings currently in use, the surface facing the driver consists of the textured skin, essentially without any cells, of a relatively soft expanded plastic molded around a hard and dimensionally stable main part. In various ways, such coverings allow, without any engineering complications worth mentioning, compliance with the contradictory requirements for adequate rigidity on the one hand and on the other for reliable opening when the airbag is needed. Still, when separate covers of real or imitation leather are employed, the compromise imposed by effective design of the break-open line entails considerable problems in that two different materials have to be taken into consideration. Their combined strength should not be enough to prevent the area from ripping open and their individual strengths should be enough to prevent it from ripping or breaking open unnecessarily subject to normal use throughout the life of the vehicle. Leather, a natural product, has in contrast to synthetic products a widely dispersed specific strength that extensively depends on temperature, humidity and can change considerably with age. It is accordingly extremely difficult to provide covers of real leather with a well defined long-term line-of-separation rip-open characteristic.
Plastic imitation leathers with a textured surface are of course less sensitive, although they have considerable tolerances in their specific strength, and can result in similar although less serious problems.
Covers of leather with separation areas in the form of punched-through areas the size of the rip-open flaps with strips of thin paper stitched to the back and extending across the incision to create the break-open line have accordingly been proposed (German 4 035 975 C2). Here, the desired specific rip-open resistance along the break-open line is that of the paper rather than that of the leather. Such resistance is obviously easier to reproduce in paper than in leather. Still, whether this approach is satisfactory in the final analysis depends on whether the paper itself exhibits the desired properties and whether they can be ensured throughout the life of the vehicle. Furthermore, this method of manufacture is very labor-intensive and must be carefully controlled to ensure that the paper is reliably attached to the leather. Finally, the perforations necessarily produced by the stitching represent an incalculable hazard.